Actuatable occupant restraint systems for vehicles are known in the art. One particular type of actuatable occupant restraint system includes an inflatable air bag mounted within the occupant compartment of the vehicle. The air bag has an associated, electrically actuatable ignitor, referred to as a squib. The system further includes one or more crash sensors for sensing the occurrence of a vehicle crash condition. Known arrangements include a series connected mechanical inertia switch, squib, and an electric switch, such as a transistor, connected across a source of electrical energy. An accelerometer is connected to a controller which is, in turn, connected to the electric switch. The controller monitors the accelerometer and, in response thereto, determines if a crash event is occurring. When a crash event occurs requiring deployment of the air bag, the inertia switch closes and the electric switch is closed by the controller resulting in an electric current of sufficient magnitude and duration to be passed through the squib to ignite the squib. The squib, when ignited, ignites a combustible gas generating composition and/or pierces a container of pressurized gas which inflates the air bag.
An inertia switch crash sensor is typically mounted to the vehicle frame and includes a pair of mechanically actuatable switch contacts and a resiliently biased weight. The biased weight is arranged such that when the vehicle decelerates, the weight physically moves relative to its mounting. The greater the amount and duration of the deceleration, the further the weight moves against the bias. The switch contacts are mounted relative to the biased weight such that, when the weight moves a predetermined distance, the weight moves over or against the switch contacts causing them to close. The switch contacts, when closed, connect a squib to one terminal of a source of electrical energy.
An electronic crash sensor for use in an actuatable occupant restraint system includes an electrical transducer or accelerometer for sensing vehicle deceleration. The accelerometer provides an electrical signal having a characteristic indicative of the vehicle's deceleration. A controller, such as a microcomputer, monitors the accelerometer output, evaluates the accelerometer signal, and controls actuation of the restraining device in response thereto.
One known controller evaluation process includes integrating the accelerometer output signal. The integral of the accelerometer output signal is indicative of the vehicle crash velocity. If the output of the integrator exceeds a predetermined velocity threshold value, an electrically controlled switch is closed which connects the squib to one terminal of an electrical energy source.